Fix corruption of encoding name string

[Bug #20595]

enc_set_default_encoding will free the C string if the encoding is nil,
but the C string can be used by the encoding name string. This will cause
the encoding name string to be corrupted.

Consider the following code:

    Encoding.default_internal = Encoding::ASCII_8BIT
    names = Encoding.default_internal.names
    p names
    Encoding.default_internal = nil
    p names

It outputs:

    ["ASCII-8BIT", "BINARY", "internal"]
    ["ASCII-8BIT", "BINARY", "\x00\x00\x00\x00\x00\x00\x00\x00"]

Co-authored-by: Matthew Valentine-House <matt@eightbitraptor.com>

0 files changed, 0 insertions, 0 deletions